I have SBS 2003 and am trying to re-install BES Express 5.0.3, however, the install fails almost immediately!

I get as far as selecting 'English' and continuing when selecting BESAdmin and the domain. Then I get the 'bar' going across the screen and then disappearing when it gets half way!

I've gone through the following at least a thousand times...... (or it seems like it)

I've been trawling the forums for 2 days now and following dozens of recommendations without success.

My BESAdmin account is an administrator of the server (local admin) but is not a domain admin (I've tried that).
I have SQL 2005 and 2008 installed (running other things).
I've stripped all mention of RIM from the registry.
I've removed all mention of RIM from folders in 'Program Files' etc.